The present invention relates to an eco-friendly method of preparation of high purity tetrabromobisphenol-A.
Tetrabromobisphenol-A, (CH3)2C(C6H2Br2OH)2 (TBBPA, 79-94-7) is an -important substance among various bromo compounds. It is a bromo derivative of bisphenol-A (BPA). It is used as a flame retardant with over one-third of the total brominated flame-retardant because of high stability and suitability as an additive and reactive compound. TBBPA is also used in the preparation of acrylonitrile butadiene styrene (ABS) polymer as well as in the preparations of epoxy and polycarbonate resins. These resins in turn are widely used for the manufacture of electronic equipment, in particular of computer-printed circuit boards. The resins are also used as fire retardant in the manufacture of coatings, plastics, paints, adhesives and laminates as the high level activity of TBBPA allows it to be used at relatively low loading, translating to a greater retention of the physical properties of the base polymer.
Reference may be made to K. Matsuda, M. Sugino and S. Kaji Japan, Kokai 74,108,003, Cl. 16 B21, Oct. 14, 1974 wherein TBBPA was prepared by reacting liquid bromine with BPA in methanol over three hours at 10-30xc2x0 C. The solution was then kept at 44-45xc2x0 C. for 3 h, treated with 383 ml of 98% H2SO4 over 40 min at 20xc2x0 C. and cooled to obtain the product. Nitrogen was-bubbled throughout to separate the by-product methyl bromide. The drawback is that it uses liquid bromine as brominating agent. Liquid bromine is a highly corrosive fuming liquid and air pollutant. Hence, it requires special equipment for its transport or storing and it needs safety measures. Thus, the method is convenient only to the bromine manufacturers. Besides these difficulties, only half of the total bromine used is utilized in the formation of product and the rest ends up as hydrobromic acid and methyl bromide as side products with the consumption of solvent which adversely affects the economics and also increases the number of unit operations. Moreover, the addition of concentrated sulfuric acid to the reaction vessel is hazardous as it is corrosive and liberates enormous heat due to dilution. Additionally, a cooling mechanism is required to absorb the heat evolved in the system, which unnecessarily enhances the product cost.
M. Ichimura, T. Nishiyama and K. Suzuki Japan Kokai 7654538, Cl. C07C25/18, May 13, 1976 prepared a high purity and less colored TBBPA by adding liquid bromine (43.68 Kg) to BPA (15.22 Kg) in tetra chloro ethylene (48 Kg) containing 0.2-1 times its weight water (66.7 Kg) at xe2x89xa640xc2x0 C. over 1 h under stirring. About 99.1% TBBPA (36 Kg) was reported obtained on heating the mixture to xe2x89xa792xc2x0 C. for 2 h with 99.6% purity. The drawback is that the liquid bromine requires special equipment to store or transport and safety measures as it is highly corrosive fuming liquid besides air pollutant. Also, it liberates hydrobromic acid as side product, which is not desired and has to be recycled with some more additional unit operations. Moreover, the heating of the reaction mixture to xe2x89xa792xc2x0 C. for 2 h is energy intensive and thus increases the production cost.
D. R. Brackenridge U.S. Pat. No. 4,013,728, Cl. 260619A; C07 C37/00, Mar. 22, 1977 reported the preparation of TBBPA by adding the liquid bromine into BPA in 75-95% (w/w) aqueous acetic acid at 0-30xc2x0 C. followed by heating to 80-120xc2x0 C. for 5 to 60 min to give 92.3% product melting at 180-182xc2x0 C. The drawbacks of this method are that both the liquid bromine and the solvent acetic acid are toxic and are air pollutants. The heating step after the addition of liquid bromine enhances the production cost. Additionally, hydrobromic acid is obtained as the byproduct, which has to be recovered from the solvent, and processed for its further use.
H. Jenkner and R. Strang Ger. Offen. 2,613,969, Cl. C07 C39/24, Oct. 6, 1977 reported a procedure for obtaining TBBPA. According to them, to a suspension of 171 parts by weight of BPA in 300 parts by volume of 1,1-dibromo ethane and 300 parts by volume of an aqueous solution containing 80 parts by weight of sodium bromate and 53 parts by weight of sodium bromide, liquid bromine (245 parts by weight) was added over 3 h at 28xc2x0 C. under stirring to give 269 g TBBPA from the organic phase. The aqueous phase was restored to its original composition via an electrolytic process. The mother liquor from the initial preparation was added and the process was repeated without the need of an additional 1,1-dibromo ethane to give a total yield of 97% TBBPA. The drawback is that it uses 2 equivalents of liquid bromine, 1 equivalent of sodium bromide and 0.47 equivalents of sodium bromate as brominating agent. About 1.5 equivalents of bromine in the form of sodium bromide or hydrobromic acid remained unused in the reaction. Additionally this method requires an electrolytic treatment to the aqueous layer to restore to its original composition for reuse in the succeeding batches and requires special equipment and safety measures to store and transport the liquid bromine.
J. Swietoslawski, A. Silowiecki, A. Ratajczak, B. Nocon and Z. Baniak Ger. Offen. 2,718,997, Cl. C07 C39/24, Nov. 17, 1977 reported the preparation of TBBPA wherein 100 g of liquid bromine was added to a solution of 68.4 g BPA in 125 ml of methanol containing 11.1 ml of concentrated sulfuric acid over 30 min at 30-35xc2x0 C. followed by 86 ml of 50% aqueous sodium chlorate over 45 min at 35-40xc2x0 C. The solution is stirred for 2 h at 40-45xc2x0 C. and cooled to 15xc2x0 C. to obtain 148 g of TBBPA in 97% yield. The main drawbacks with this method are that both the liquid bromine and sodium chlorate are highly corrosive. Liquid bromine requires special equipment and safety measures to stop the air pollution and to avoid accidents. The use of non-bromo compound as an oxidizing agent to utilize the byproduct is an energy intensive step and it releases unwanted side product and further complicates the purification step.
W. Baumann, A. Block, I. Boehnke, J. Fiernow, H. Fischer, P. Franke E. Heynisch, D. Timm and H. Weber Ger. East DD 159,066, Cl. C07 C39/367, Feb. 16, 1983 and Ger East DD 211,781, Cl. C07 C39/367, Jul. 25, 1984 prepared TBBPA by the bromination of BPA with bromine liquid in methylene chloride and water medium. In this method, the organic layer was separated from the mother liquor and treated with 10% aqueous sodium hydroxide (Ger. East DD 159,066, Cl. C07 C39/367, Feb. 16, 1983) and distilled (Ger East DD 211,781, Cl. C07 C39/367, Jul. 25, 1984) to get solvent for the reuse. The drawback is that the handling of liquid bromine is hazardous as it is highly corrosive and air pollutant and also 50% of total bromine used is converted into hydrobromic acid, which increases the process steps and thus effects, the cost of production. The neutralization of hydrobromic acid existing in the organic layer with 10% sodium hydroxide and the electrolytic treatment of the aqueous layer for the reuse in succeeding batches are extra steps involved in addition to the problems associated with the corrosive liquid bromine.
I. Bohenke, U. Geyer and D. Timm German East DD 211,782, Cl. C07 C39/367, Jul. 25, 1984 brominated 175 g of BPA with 462 g of bromine in a mixture of 100 ml toluene, 200 ml methylene chloride and 600 ml water under stirring at 43xc2x0 C. Methylene chloride (198 ml) was distilled and the product (398.5 g, m. p. 153-161xc2x0 C.) was filtered from the remaining at 10xc2x0 C. Apart from the use of liquid bromine, only 79.3% of TBBPA was obtained along with the products like di- (3.6%) and tri-bromo (17.1%) derivatives. The drawback is that it uses liquid bromine, which is corrosive and air pollutant and requires special equipment for storing and transporting. Hydrobromic acid is produced as an undesired byproduct by the consumption of 50% of the total bromine used in the operation and needs additional unit operations to recycle. Besides these problems, the yield of TBBPA is only 85% and is contaminated with di- (3.6%) and tri-bromo (17.1%) derivatives of bisphenol-A. Moreover, the filtration of the product at low temperatures requires special arrangements, which adds to the total cost of TBBPA.
U. Geyer, D. Timm and I. Boehnke Ger. East DD 808,344, Cl. C07 C39/367, May 2, 1984 brominated 175 g BPA with 458 g of bromine in (150 g) cyclohexane and (150 g) methylene chloride and (400 ml) water. A mixture of 0.3% mono-, 5%. di- and 18% tri-bromo derivatives along with 76.7% TBBPA was reported produced. The drawback with this technique is that it uses liquid bromine as brominating agent, which is corrosive and requires special equipment and safety devices. Half of the total bromine used in this method is converted to the undesired hydrobromic acid, which requires additional unit operations for recycling and thus affects the cost of TBBPA largely. Moreover, the intermediate products such as mono-, di-, and tri-bromo bisphenol-A whose separation from TBBPA is a difficult process. This method requires two organic solvents cyclohexane and methylene chloride.
I. Israeli IL 64,410, Cl. C07 C39/367, Mar. 31, 1985 obtained a highly pure TBBPA by the bromination of 320 g BPA with the addition of 465 g bromine liquid, 60 ml water, 2 g of 8% dodecylbenzene sulfonate, 185 g of 40% aqueous hydrogen peroxide and 750 ml of methylene chloride saturated with TBBPA. The drawback with this technique is that it uses liquid bromine as brominating agent, which is corrosive and requires special equipment and safety devices. Hydrogen peroxide used, as an oxidizing agent is a non-bromo compound and it disproportionate at room temperature to oxygen and water spontaneously. Thus, more than the stoichiometric amount of hydrogen peroxide is to be added at every batch. Ultimately, this enhances the cost of TBBPA production.
T. Ogata M. Aritomi and C. Asano Japan Tokyo Tokyo Koho JP 62,221,645; Cl. C07 C39/367, Sep. 29, 1987 reported the procedure for the preparation of TBBPA wherein liquid bromine was added drop wise to a dispersion of BPA in water-carbon tetrachloride at 15-18xc2x0 C. over 1.5 h to get 99.2% TBBPA after heating to 70-72xc2x0 C. for 2 h. The drawback with this technique is that it uses liquid bromine which is corrosive and toxic and it requires special equipment and safety devices. Half of the total bromine used in this method is converted to hydrobromic acid, which increases some more unit operations. Heating the reactants to 70-72xc2x0 C. after the bromine addition is enhances the production cost.
C. Asano Japan Kokai Tokyo Koho JP 63,316,74, Cl. C07 C39/367, Dec. 26, 1988 obtained 99.2% pure TBBPA in a multi -stage reaction. According to him the addition of 142 g bromine over 2 h to a 50 g of BPA in 175 g chloro benzene and 125 g water at 15-20xc2x0 C. gives 117.9 g of crystalline TBBPA containing 4 ppm bromide after heating the mixture at 15-20xc2x0 C. for 1.5 h, stirring the mixture for 30 min at 80xc2x0 C., adding 0.6 g of 60% hydrazine hydrate, heating to 90xc2x0 C., separating the aqueous phase, washing the organic phase, depressing the organic phase to remove 62 g chloro benzene, and cooling the organic phase to 25xc2x0 C. The drawbacks are that it requires corrosive liquid bromine for the bromination reaction and also hydrazine hydrate to reduce the impurities. The step heating to 80 and 90xc2x0 C. adds to the cost of TBBPA. Further, this method liberates hydrobromic acid as the side product, which requires additional unit operation for reuse.
R. P. Pandya, M. M. Pandya, J. K. Langalia, P. R. Mehta and M. M. Taqui Khan Indian IV 162,522, Cl. C07 C27/00, Jun. 4, 1988 obtained 5 Kg of TBBPA (mp 181xc2x0 C.) by adding 8.842 Kg of liquid bromine under stirring at xe2x89xa640xc2x0 C. to 3 Kg of BPA dissolved in 3.5 1 of ethyl alcohol and 1.4 1 of water containing 1 g of ferric chloride as a catalyst. The drawbacks of this method are that it uses corrosive liquid bromine as brominating agent and losses 50% bromine in the formation of hydrobromic acid which requires additional unit operations to reuse. Moreover, the contents have to be stored for 24 h after the completion of the bromine addition, which brings down the production rate. On the other hand, the contents have to be diluted with large volume of water to recover maximum quantity of TBBPA. As a result, the process of separation of hydrobromic acid and recovery of alcohol from the mother liquor become difficult. Further, the catalyst iron adds, as impurity to the final product and thus it is difficult to get polycarbonate grade product by this method.
E. Walter Ger. Offen. DE, 3,935,224, Cl. C07 C39/367, Apr. 25, 1991 claimed the formation of TBBPA in the bromination of BPA with liquid bromine, hydrobromite /hydrogen bromide in an organic solvent like chloro benzene. 50% of aqueous hydrogen peroxide was added additionally whereby the hydrobromic acid produced during the reaction was oxidized to bromine. The TBBPA thus formed was heated to dissolve in the organic phase which was separated and washed with 1 M aqueous sodium sulfite and twice with water at 80xc2x0 C. The drawback of this method is that the brominating agent is liquid bromine. Moreover, it requires hydrogen peroxide, which decomposes spontaneously at room temperature. The purification of TBBPA with aqueous sodium sulfite and water at 80xc2x0 C. would add to the cost.
H. Eguchi, M. Kubo N. Nagasaki and K. Kunimoto Eur. Pat. 472,395, Cl. C07 C37/62, Feb. 26, 1992 patented the process of preparation of TBBPA wherein (58.8 g) BPA was brominated with (163 g) liquid bromine in (300 g) methanol. Additionally, they added 40.6 g of 36% hydrochloric acid to yield 96.5% product with 98.7% purity. The drawback is that it uses liquid bromine as a brominating agent, which requires special equipment and safety devices. In addition, the mother liquor obtained after the separation of product is highly acidic due to hydrochloric acid which has to be destroyed for its safe discharge. The undesired byproducts methyl bromide (0.3 g) and hydrobromic acid consume more than 50% bromine used, thereby reducing the bromine atom efficiency. B.G. Mckinnie, G. L. Sharp and R. E. William U.S. Pat. No. 5,283,375, Cl. 568-726 C07 C39/387, Feb. 1, 1994 prepared the TBBPA by adding 3.9-4.2 moles of bromine to 1 mole of BPA dissolved in 25-43 moles of methanol containing less than or equal to 5% water at 0-40xc2x0 C. and diluting subsequently with water. The product was purified to have less than or equal to 20-ppm ionic impurities. The drawbacks of this process are that it uses corrosive bromine as brominating agent and half of the brominating agent ends-up as hydrobromic acid. Further, the reaction mixture has to be diluted extensively to obtain maximum TBBPA. As a result, the recovery of organic solvent and the byproduct hydrobromic acid from the filtrate to make the process cost benefit becomes quite expensive.
S. Armstrong U.S. Pat. No. 5,475,153, Cl. 568-726, C07 C39/367, Dec. 12, 1995 brominated the BPA with liquid bromine at 15-25xc2x0 C. in C3-C5 alkanols and water to suppress the formation of alkyl bromides and then heated to 55-70xc2x0 C. to get 98% pure TBBPA (mp, 180xc2x0 C.). Hydrogen peroxide was combined with the reactants to reduce the amount of bromine required. The drawbacks of this are that it uses liquid bromine as brominating agent and requires a non-bromo compound, which decomposes spontaneously at room temperature to use the hydrobromic acid formed during the reaction.
The main object of the present invention is to provide a method of preparation of tetrabromobisphenol-A wherein the use of corrosive liquid bromine is eliminated and obviates the drawbacks as detailed above.
Another object of the present invention is to use the combination of bromide and bromate ions as brominating agent.
Yet, another object of the present invention is to use the aqueous mixtures of bromide and bromate salts obtained as intermediate in bromine manufacture.
Yet, another object of the present invention is to use bromate ion both as bromine source and as stable and non-contaminating oxidizing agent to achieve 100% bromine atom efficiency.
Yet, another object of the present invention is to use hydrobromic acid both as bromine source and as mineral acid to minimize requirement of additional acid in the reaction.
Still another object is to recycle the organic layer from the reaction mixture in subsequent batches to minimize processing time, maximize yield and minimize effluent discharge.
The aim of present invention is to provide an eco-friendly method of preparation of a colorless tetrabromobisphenol-A with very good yields and maximum bromine efficiency. It has been surprisingly found that the 2:1 molar combination of bromate and bromide ions in the presence of a strong mineral acid rapidly produces-bromine which is completely utilized in the in situ bromination of bisphenol-A with minimum precautions and no special devices essential when liquid bromine is used. The present process is rapid, specific, environmental friendly and cost-effective giving high purity tetrabromobisphenol-A which melts at 180xc2x12xc2x0 C. The method gives 50-70% tetrabromobisphenol-A in first batch and 90-100% when the spent organic layer is recycled. The reaction takes 4-5 h. The isolated product obtained does not require no further recrystalization while the aqueous layer can be discharged safely. Such a compound is useful as a flame retardant and also in the preparation of acrylonitrile butadiene styrene polymer as well as in the epoxy and polycarbonate resins.